Certain abbreviations that may be found in the description and/or in the Figures are herewith defined as follows:
3GPPThird Generation Partnership ProjectCAZACconstant-amplitude zero auto-correlationCDMcode division multiplexingCDMAcode division multiple accessCMcubic metricCPcyclic prefixCQIchannel quality indicatorDFTdiscrete Fourier transformE-UTRANevolved UTRANFDMfrequency division multiplexingFDMAfrequency division multiple accessFFTfast Fourier transformIFFTinverse FFTLBlong blockLTElong term evolutionNode BBase StationeNode BEUTRAN Node B (eNB)OFDMorthogonal frequency domain multiplexPARpeak to average ratioPRBphysical resource blockPUCCHphysical uplink control channelQPSKquadrature phase shift keyingRRCradio resource controlRSreference signalRUresource unitSCsubcarrierSC-FDMAsingle carrier, frequency division multiple accessSFspreading factorSNRsignal to noise ratioTTItransmission time intervalUEuser equipmentULuplinkUTRANuniversal terrestrial radio access networkDFT-S-OFDMdiscrete Fourier transform spread OFDM (SC-FDMA based on frequency domain processing)WCDMAwideband code division multiple access
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE) is currently under discussion within the 3GPP. The working assumption is that the DL access technique will be OFDMA, and the UL technique will be SC-FDMA.
Reference can be made to 3GPP TR 36.211, V1.0.0 (2007-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and Modulation (Release 8), for a description in Section 6 of the UL physical channels.
Reference can also be made to 3GPP TR 25.814, V7.1.0 (2006-09), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical layer aspects for evolved Universal Terrestrial Radio Access (UTRA) (Release 7), such as generally in section 9.1, for a description of the SC-FDMA UL of E-UTRA.
FIG. 1A reproduces FIG. 12 of 3GPP TS 36.211 and shows the UL slot format for a generic frame structure.
As is described in Section 9.1 of 3GPP TR 25.814, the basic uplink transmission scheme is single-carrier transmission (SC-FDMA) with cyclic prefix to achieve uplink inter-user orthogonality and to enable efficient frequency-domain equalization at the receiver side. Frequency-domain generation of the signal, sometimes known as DFT-spread OFDM (DFT S-OFDM), is assumed.
FIG. 1B shows the generation of pilot samples. An extended or truncated Zadoff-Chu symbol sequence is applied to an IFFT block via a sub-carrier mapping block. The sub-carrier mapping block determines which part of the spectrum is used for transmission by inserting a suitable number of zeros at the upper and/or lower end. A CP is inserted into the output of the IFFT block.
In the PUCCH sub-frame structure for the UL control signaling seven SC-FDMA symbols (also referred to herein as “LBs” for convenience) are currently defined per slot. A sub-frame consists of two slots. Part of the LBs are used for reference signals (pilot long blocks) for coherent demodulation. The remaining LBs are used for control and/or data transmission.
It is pointed out that there are different slot formats that are applicable for the exemplary embodiments of this invention that are described below. Reference in this regard may be made to Table 1 “Resource block parameters” on page 10 of 3GPP TR 36.211, V1.0.0 (2007-03).
The current working assumption is that for the PUCCH the multiplexing within a PRB is performed using CDM and (localized) FDM is used for different resource blocks. In the PUCCH the bandwidth of one control and pilot signal always corresponds to one PRB=12 SCs.
It should be noted that it has yet to be determined whether to support 18 SCs on the PUCCH. However, for the purposes of describing the exemplary embodiments of this invention below the exact number of SCs does not matter (e.g., whether there are 12 or 18 SCs that are supported).
Two types of CDM multiplexing are used both for data and pilot LBs. Multiplexing based on the usage of cyclic shifts provides nearly complete orthogonality between different cyclic shifts, if the length of cyclic shift is larger than the delay spread of radio channel. For example, with an assumption of a 5 microsecond delay spread in the radio channel, up to 12 orthogonal cyclic shifts within one LB can be achieved. Sequence sets for different cells are obtained by changing the sequence index.
Another type of CDM multiplexing may be applied between LBs based on orthogonal covering sequences, e.g., Walsh or DFT spreading. This orthogonal covering may be used separately for those LBs corresponding to the RS and those LBs corresponding to the data signal. The CQI is typically transmitted without orthogonal covering.
Of particular interest to the exemplary embodiments of this invention is control channel signaling and, in particular, the use of the PUCCH.
More specifically, the exemplary embodiments of this invention pertain to ACK/NACK signaling. The ACK/NACK signaling format has been determined and is shown in FIG. 2 (originally presented in 3GPP TSG RAN WG1 Meeting #47bis, Sorrento, Italy, Jan. 15-19, 2007, “CDM based Control Signal multiplexing w/ and w/o additional RS”, Nokia, R1-070395.
In this approach the ACK/NACK is transmitted by means of a modulated CAZAC sequence, and the ACK/NACK signals of different UEs can be orthogonally multiplexed within the pilot/data blocks using different cyclic shifts of the same base CAZAC sequence. The length of the CAZAC sequence is equal to 12 symbols. Also, coherent transmission with three reference signal (RS) blocks and four data blocks (ACK/NACK) is applied. In addition, block level spreading with SF=¾ is applied to the RS/data blocks.
Different ACK/NACK UEs are multiplexed by means of CDM. As can be seen in FIG. 3, there are in total 12×3=36 code resources available for reference signals and 12×4=48 resources for data signals. Due to the intra-cell orthogonality issue, only part of the code resources can be used in practice (e.g., one half or one third).
In this case these resources are not allocated explicitly because of the fact that the fixed size resource is always needed in certain situations. Instead, implicit resource allocation is used. It has been determined at RAN1 meeting (#49, Kobe) that for non-persistent scheduling the ACK/NAK resource is linked to the index of the control channel used for (DL) scheduling (see 3GPP TSG RAN WG1 Meeting #49, Orlando Fla.-USA, 25-29 Jun. 2007, “Draft Report of 3GPP TSG RAN WG1 Meeting #49 v0.3.0 (Kobe, Japan, 7-11 May 2007), Section 7.13.2).
The actual need for implicit ACK/NACK resources depends on the number of scheduled UEs in the DL (e.g., bandwidth and scheduling strategy). In a practical sense the ACK/NACK capacity is limited by the inter-cell interference. In general, about 10-12 ACK/NACK UEs/RU/cell can be supported (at least in the DL SIMO case). Reference in this regard may be made to 3GPP TSG RAN WG1 Meeting #47bis, Sorrento, Italy, Jan. 15-19, 2007, “ACK/NACK coverage in the absence of UL data”, Nokia, R1-070393.
It has been determined in 3GPP that implicit ACK/NACK resources are configured by means of RRC signaling. However, it can be seen that a number of parameters are needed to characterize one implicit ACK/NACK resource. An implicit ACK/NACK resource here means an ACK/NACK resource that is allocated via implicit signaling, i.e., there is no explicit signaling that tells to the UE which ACK/NACK resource to use for acknowledging a DL transmission. Instead, the ACK/NACK resource is tied to the DL control channel index and is thus signaled implicitly (e.g., by the control channel index). First, static parameters are needed, such as the frequency allocation of the ACK/NACK resource, i.e., the RU for the 1st slot and for the 2nd slot (see FIG. 1). Also needed is the spreading factor of RS blocks (e.g., 3), with two alternatives in the FDD mode (depending on the CP length). Also needed is the spreading factor of data blocks (e.g., 4), with two alternatives in the FDD mode (depending on the CP length). Also needed is the length of the CAZAC sequence (12 frequency bins), with 18 bins being a possible candidate. The static parameters are typically defined in the standard specification.
Second, semi-static parameters are needed, such as the base sequence of the frequency domain CAZAC code (typically separately for the pilot and the data), the base sequence of the block level code (typically separately for the pilot and the data), the cyclic shift allocation for the frequency domain CAZAC code (typically separately for the pilot and the data), the cyclic shift allocation for block level code (typically separately for the pilot and the data), information concerning cyclic shift hopping (typically separately for the pilot and the data), as well as information concerning possible CAZAC sequence hopping (it is for future study whether this feature is supported). The semi-static parameters are typically signaled using higher layer signaling (e.g., RRC signaling) to each UE, or they may be broadcast to the entire cell via a broadcast channel.
It can be noted that most of these parameters are cell-specific, including all of the static parameters, the base sequence indices (both in the frequency and block domains) and the shift/sequence hopping related parameters.
The largest burden is related to the signaling of the cyclic shift resources, which are resource specific. Note that 12 bits are needed to characterize cyclic shifts of one implicit ACK/NACK resource, where six bits are needed to characterize the ACK/NACK RS resource (12*3 available code channels) and an additional six bits are needed to characterize the ACK/NACK data resource (12*4 code channels).
It has been assumed thus far that all of the cyclic shifts of all available implicit ACK/NACK resources are explicitly signaled by means of RRC signaling. This corresponds to a signaling burden with 12, 18 and 36 implicit ACK/NACK resources (there are thus 12, 18 or 36 ACK/NACKs possible to send per TTI) that is equal to 144 bits, 216 bits and 432, respectively. As can be appreciated, this amount of signaling load can be disadvantageous.